Field
Indication of delivery-path information may benefit various communication systems. For example, wireless communication systems may benefit from per-protocol data unit delivery-path indication to data recipient.
Description of the Related Art
In the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) air-interface protocol stack, the Packet Data Convergence Protocol (PDCP) currently lies above the Radio Link Control (RLC) protocol. PDCP is currently defined by third generation partnership project (3GPP) technical specification (TS) 36.323, which is hereby incorporated herein by reference. RLC is defined by 3GPP TS 36.322, which is hereby incorporated herein by reference.
For PDCP, the listed ‘Services expected from lower layers’ comprise among others: acknowledged data transfer service, including indication of successful delivery of PDCP PDUs.
The RLC protocol [TS 36.322] uses the reordering timer, with RRC-configurable expiry time, to infer when a packet has been lost at MAC layer instead of still undergoing possible HARQ retransmissions: the timer is started when a gap in received PDUs is observed, and if the timer expires the lost packet is NACKed to the peer RLC entity (acknowledged mode), or the gap in packets is ignored when delivering data to higher layer (unacknowledged mode).
Related to studies on dual connectivity in E-UTRAN, FIG. 1 illustrates distributed radio link control and independent radio link control options. As shown in FIG. 1, in a distributed radio link control model, the RLC PDUs are assigned by the macro eNB and a subset is sent to the pico eNB. The RLC acknowledged mode PDU resegmentation mechanism, used by Rel-10 for RLC retransmissions, is repurposed at the slave eNB to fit AMD PDU segments into the scheduled transport block. Moreover, RLC retransmissions may only be handled at the macro eNB.
In an independent-RLCs model, distinct RLC entities at macro and pico handle different sub-bearers. Moreover, UE protocol architecture is different from Rel-10 CA.
Moreover, with respect to the independent-RLCs option, the master node may be provided the following feedback: whether each PDCP PDU was received by the slave node over the “X2” interface; and which PDCP PDUs the UE has indicated as successfully received to know which packets the network-side PDCP can discard.
The above will be provided if the following feedback mechanisms are in place: acknowledged data transfer over the “X2” interface, which is not present in the current data transfer over X2: see 3GPP technical specification (TS) 36.424); acknowledged data transfer over each of the RLC bearers serving the PDCP bearer, as currently specified in the RLC protocol; and the indications of successful downlink delivery of PDCP PDUs, from the slave node to the master node.
Alternatively, a continuously running ARQ mechanism can be adopted at PDCP level, which is not currently in place in the PDCP protocol, which may render all three items above unnecessary. This also implies that the RLC bearers serving the acknowledged-mode PDCP bearer could run in unacknowledged mode.